Superatmospheric pressure used to improve the sensitivity of silver halide emulsions



nited States Patent Offi 3,542,557 Patented Nov. 24,- 1970 Int. Cl. G03c 1/08 U.S. Cl. 96-107 11 Claims ABSTRACT OF THE DISCLOSURE An improved method for making a photographic silver halide emulsion, the improvement comprising subjecting the liquid silver halide emulsion to a superatmospheric pressure of at least 30 p.s.i. for at least 0.5 hour before coating said emulsion on a support.

This invention relates to photographic materials, and more particularly to methods for increasing the gamma and sensitivity of photographic silver halide emulsions. It also relates to methods for preparing photographic elements which exhibit increased sensitivity and gamma.

As used herein and in the appended claims, the term sensitivity refers to the speed sensitivity of the emulsion, rather than spectral or optical sensitivity of the emulsion.

One object of this invention is to provide a method for increasing the sensitivity of photographic emulsions.

Another object of this invention is to provide a method for increasing the gamma of silver halide emulsions.

A still further object of this invention is to provide photographic emulsions exhibiting increased speed and gamma.

Still another object of this invention is to provide a method for preparing photographic elements featuring increased speed and gamma.

Other objects of this invention will be apparent from the disclosure herein and the appended claims.

We have found that if liquid emulsions are subjected to superatmospheric pressure, an unexpectedly high increase in sensitivity is obtained, and a totally unexpected in crease in gamma is produced.

In one embodiment of this invention, the gamma and sensitivity of a liquid, light-sensitive silver halide emu sion is increased by the method which comprises subjecting the emulsion to superatmospheric pressure.

In another embodiment of this invention, photographic elements are prepared by subjecting a liquid, light-sensitive silver halide emulsion to superatmospheric pressure, and coating the emulsion on a suitable support.

Advantageously, the treatment is conducted at a pressure and for a time sufiicient to effectively increase the sensitivity and gamma of the emulsion. Generally, it is desirable to treat the emulsion to provide at least a 100% increase in sensitivity and to increase the gamma at least twofold. The emulsion is treated in accordance with the invention prior to exposure. Preferably, the emulsion is subjected to pneumatic pressure prior to coating.

In accordance with the invention, the emulsion can be subjected to pressure in any convenient manner. It has been found highly desirable to subject the emulsion to pneumatic pressure. This can be conveniently accomplished by placing the emulsion in a suitable container, and introducing a suflicient quantity of a gas which does not exert detrimental elfects on the emulsion, to raise the pressure within the container to superatmospheric pressure. Preferably, the emulsion is agitated sufliciently to prevent settling. When this technique is employed, a wide variety of gases can be used, such as nitrogen, carbon dioxide, hydrogen and helium, and inert gases such as neon, argon, krypton and xenon.

The time, temperature and pressure employed can be varied over a wide range, depending upon the amount of increase in sensitivity and gamma desired. The effects obtained appear to be interdependent upon the temperature, pressure and residence time. Good results can be obtained, for example, by subjecting the liquid emulsion to superatmospheric pressure, such as at least 30 p.s.i. and preferably at least 50 p.s.i. to about 3,000 to 6,000 p.s.i., for times ranging from about /2 hour to several days. Generally, pressure treatment for times of 1 to 24 hours gives good results. The temperature also can be varied over a wide range, such as from 35 to C. Temperatures of 40 to 65 C. are quite suitable.

The pressure treatment of this invention is effective to raise the sensitivity and gamma of a wide variety of silver halide emulsions. The silver halide may be silver chloride or silver bromide, or mixed halides such as silver chlorobromide, silver bromoiodide or silver chlorobromoiodide. The emulsions can be of the negative type or they may be direct positive emulsions which may be light fogged or emulsions fogged with chemicals, e.g., reducing agents or a combination of reducing agent and a compound of a metal more electro-positive than silver. For example, the invention is useful with reversal emulsions fogged with formaldehyde or thiourea-dioxide and a gold salt such as potassium chloroaurate. The invention is also useful with emulsions which have high internal sensitivity and low surface sensitivity.

The silver halide can be dispersed in any suitable dispersing agent such as gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe US. Pat. 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 19-26% as described in U.S. Pat. 2,327,808 of Lowe and Clark, issued Aug. 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy U.S. Pat. 2,322,085, issued June 15, 1943; a polyacrylamide having a combined acrylamide content of 30-60% and a specific viscosity of 025-15 on an imidized polyacrylamide of like acrylamide content and viscosity as described in Lowe, Minsk and Kenyon U.S. Pat. 2,541,474, issued Feb. 13, 1951; zein as described in Lowe U.S. Pat. 2,563,791, issued Aug. 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith U.S. Pat. 2,768,154, issued Oct. 23, 1956; or containing cyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetate copolymer as described in Unruh, Smith and Priest U.S. Pat. 2,808,331, issued Oct. 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in U.S. Pat. 2,852,382, of Illingsworth, Dann and Gates, issued Sept. 16, 1958.

The emulsions treated in accordance with this invention can contain the chemical sensiltizers, stablizers, speed increasing compounds, plasticizers, hardeners, coating aids and spectral sensitizers referred to in columns 10 through 12 of Beavers U.S. Pat. 3,039,873, issued June 19, 1962. Such addenda can be added before or after the pressure treatment in accordance with the invention.

The emulsions treated in accordance with this invention can be coated on any suitable support, such as film base, e.g., a cellulose ester such as cellulose acetate or cellulose acetate butyrate, a polyester such as polyethylene terephthalate, a polycarbonate film or a polyolefin (e.g., polyethylene or polypropylene). The emulsions can also be coated on other supports, such as paper, baryta coated paper, polyethylene or polypropylene coated paper, which can be electron bombarded to promote emulsion adhesion.

This invention will be further illustrated by the following examples which show pneumatic pressure treatment of liquid emulsions.

EXAMPLE 1 A coarse-grained (average size approximately 1 micron) gelatin silver bromiodide emulsion (approximately 5% of the silver halide being silver iodide), was placed in a high pressure bomb which was maintained at 40 C. By pumping nitrogen into the bomb, the pressure was increased to 2,000 pounds per square inch and held for twenty-four hours during which time the bomb was rocked to prevent settling of the emulsion. The pressure was released and the emulsion removed from the bomb. The sensitivity of this emulsion, B was compared to the original emulsion, A and the emulsion held for twentyfour hours at 40 C. without pressure, C, by preparing plates from the emulsions, exposing and processing for four minutes in Kodak developer D-19. The sensitometrics obtained are shown in Table I.

TABLE I Emulsion Relative speed Gamma Gross tog The above example demonstrates the unexpectedly high increase in gamma and sensitivity obtained when emulsions are treated in accordance with the invention.

The following example illustrates the increase in sensitivity of an emulsion of the type having high internal sensitivity and low surface sensitivity.

EXAMPLE 2 An emulsion was prepared by the procedure described in U.S. Pat. 2,592,250, which contained approximately 12% chloride, 87% bromide and 1% iodide. This emulsion had 'low surface sensitivity but high internal sensitivity. The emulsion was placed in a high pressure bomb, and subjected to 1850 pounds per square inch nitrogen pressure for sixteen hours at 40 C. The resulting emulsion, after coating, was sensitometrically exposed and developed for 5 minutes in Kodak developer D-19 with the results shown in columns under A in Table II. Another sample was treated in the same manner except that grams per liter hypo were added to the developer. The results are shown in the columns under B in Table II.

This type of emulsion does not ordinarily reverse in the reversal process of U.S. Pat. 2,563,785, giving a reversal D max. of approximately 0.24. It will reverse, however, to give a reversal D max. of 1.71 if a small amount of potassium iodide is added to the developer. After the pressure treatment the emulsion does reverse in the proc ess of U.S. Pat. 2,563,785, Without the added potassium iodide, to give a D max. of 2.29.

The present invention provides a method for obtaining silver halide emulsions having good sensitivity without requiring chemical sensitizers. This is advantageous in some commercial applications where it is desired to avoid fog insofar as possible. Chemical sensitizers tend to induce fog. The treatment of the present invention offers advantages over prior art pressure treatments of coated, dried-down silver halide emulsion layers. In addition, it has been found that the pressure treatment of the invention increases speed and gamma for an indefinite period. The emulsions of the invention may contain chemical and spectral sensitizers.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. In a method of making an improved silver halide emulsion, the improvement comprising the step of subjecting a liquid emulsion of silver halide to a superatmospheric pneumatic pressure of at least 30 p.s.i. for at least /2 hour before coating said emulsion on a support wherein said liquid emulsion is maintained at less than C.

2. A method according to claim 1 wherein said liquid emulsion of said silver halide is subjected to a pressure of at least 60 p.s.i.

3. A method according to claim 1 wherein said liquid emulsion of said silver halide is subjected to a pressure of about 2.000 p.s.i. for a period of about 24 hours.

4. A method according to claim 1 wherein the pneumatic pressure is achieved by introducing a gas within a container holding the emulsion, said gas being selected from the group consisting of nitrogen, carbon dioxide, hydrogen, helium, neon, argon, krypton and xenon.

5. A method according to claim 1 wherein nitrogen gas is used to achieve said superatmospheric pneumatic pressure.

6. A method according to claim 1 wherein the pressure is continued for a time sufficient to increase the sensitivity of the emulsion by at least and to raise the gamma at least twofold.

7. A method according to claim 1 wherein said silver halide comprises silver halide grains having higher internal radiation sensitivity than surface radiation sensitivity.

8. A product produced by the process of claim 1.

9. A method of making an improved silver halide emulsion comprising 1) reacting a water-soluble halide with a water-soluble silver salt in the presence of a liquid hydrophilic colloid medium to form a liquid silver halide emulsion, (2) subjecting said liquid silver halide emulsion to a superatmospheric pressure of at least 50 p.s.i. for a period of at least 0.5 hour wherein said liquid emulsion is maintained at less than 85 C. and (3) coating said emulsion on a support.

10. A method according to claim 9 wherein said liquid emulsion is subject to said superatmospheric pressure for at least 1 hour.

11. The product formed by the process of claim 9.

References Cited Properties of photographic emulsions prepared at high temperature under pressure. Shuji Umano et al.

in Chemical Abstract, vol. 47, page l2068e.

Influence of Pneumatic Pressure on Photographic Sensitivity by Choong Shin-Piaw, in Journal of the Optical Society of America, vol. 34, No. 5, May 1944, pages 285, 289.

NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner U.S. C1. X.R. 96-94 

